Baseline's Grounding Resources

Earth

What is grounding?

The National Electric Code®, Article 100 defines a ground as "a conducting connection, whether intentional or accidental, between an electrical circuit or equipment and the earth or to some conducting body that serves in place of the earth".

 

Why is grounding necessary?

Grounding protects people, protects equipment, and fulfills Baseline's extended warranty requirements. The grounding system provides a safe path for current to dissipate.

Why does Baseline have specific grounding requirements?

Proper installation of grounding rods and wire connections is essential to providing good surge suppression. While there is no technology currently available that can fully protect an irrigation system against damage from massive surges such as those caused by direct lightning strikes, outfitting your Baseline system with grounding and surge arrestors as outlined in our Surge Arrestor and Grounding Spec will protect from most if not all naturally occurring electrical surges.

 


Electrode

What is a grounding electrode?

 

A grounding electrode is a conductor in intimate contact with the earth for the purpose of providing a connection with the soil

 

The following types of grounding electrodes can be used:

  • Rods
  • Plates
  • Electrolytic electrodes

 

What is ground resistance?

Ground resistance is the measurement of the conducting connection between the grounding system and earth.

 

After you have installed your grounding system, Baseline requires that you measure the ground resistance in order to prove that each grounding point meets Baseline's specifications. Resistance readings of 5 to 10 ohms are desirable, and a reading of no more than 25 ohms is required. You should measure the system at least once a year to ensure that the resistance readings remain constant.

 

Factors that affect resistance:

  • Type of grounding electrode
  • Contact with the soil
  • Soil resistivity
  • Contact resistance
  • Conductor/bonding

Testing Ground Resistance

Ground resistance can (and should be) measured using a 3-point ground resistance tester or a clamp-on tester and one of the following methods:

 

Refer to Understanding Ground Resistance Testing by AEMC® Instruments

Grounding Electrode Tips

  • Increasing the depth to which a rod is driven can substantially reduce resistance. Doubling the rod depth reduces its effective resistance by as much has 40 percent.
  • Increasing the diameter of a rod does NOT materially reduce its resistance – in fact, doubling the diameter reduces the resistance by less than 10 percent.
  • You can use a soil resistivity test and a Grounding Nomograph to estimate the rod depth required to achieve the necessary resistance.
  • A grounding rod driven into rocky soil will only make contact on the edges of the surrounding rock, which does not provide the required intimate contact. Take steps to ensure that intimate contact is achieved and maintained. Also keep in mind that ground rods may not be practical on job sites with rocky soils.
  • When a grounding rod is driven into compacted or rocky soil, "mushrooming" can occur on both the top of the rod and the end that is being driven into the soil. A ground rod sleeve may prevent the top of a ground rod from mushrooming. However, if the end of the ground rod is mushrooming, you might need to use an advanced driven rod that is installed with a standard drill hammer.
  • After a grounding rod is driven into the soil, allow the soil to settle in order to eliminate air pockets.
  • The chassis ground on the irrigation controller can be connected to the building system ground, but DO NOT connect the two-wire ground to the building system ground. This creates a loop that causes noise and damage on the two-wire.

 

The goal is LOW ground resistance

 


connectors

Bonding Connectors

All points of connection in the grounding system must have some type of bonding connector. These can be compression connectors, mechanical connectors, or exothermic weld connectors. All compression and mechanical connectors must be suitable for direct burial.

 

The weakest link in a grounding system is usually the bonding.

 

Test the bonding connectors yearly with a micro-ohm meter. The resistance reading on these connections should be less than one milliohm.

 


Soil Resistivity

Soil resistivity is a measure of how much the soil resists the flow of electricity (or inversely, a measure of the earth's ability to conduct electricity).

 

There is a direct relationship between ground resistance and soil resistivity, i.e., lower soil resistivity results in lower ground resistance.

 

Soil resistivity is the key factor that determines what the resistance of a grounding electrode system will be and to what depth the electrodes must be driven to obtain low ground resistance. The resistivity of the soil varies widely throughout the world and changes seasonally.

 

Soil resistivity is affected by the following environmental factors:

  • Moisture content
  • Electrolyte content (minerals and dissolved salts)
  • Temperature

Testing Soil Resistivity

Soil resistivity testing is not always required, but it can be a very effective and cost/labor saving tool. The test can help you determine the rod depth required in order to achieve your desired ground resistance.

 

Soil resistivity can be tested using a 4-pole Ground Resistance Tester using the Wenner Method.

 

four-point test

 

Refer to Understanding Ground Resistance Testing by AEMC® Instruments


Testing Irrigation Wire Grounding and Measuring Ground Resistance

We recommend that you test the irrigation wire grounding at your site with a clamp-on ground resistance tester. Follow the appropriate procedures for the type of tester you are using.

Refer to Using a Clamp-On Tester to Test Ground Resistance

Download our Clamp-on Ground Resistance Worksheets (for two-wire and conventional wire)

 

We also recommend that you measure the ground resistance with a 3-point ground resistance tester. Follow the appropriate procedures for the type of tester you are using.

Refer to Measuring Ground Resistance with the 62% Method

Download our Ground Resistance Worksheets for the 62% Test


Equipment for Testing and Measuring

ground resistance tester

AEMC Digital Ground Resistance Tester (Models 4620 & 4630)

Clamp-On Ground Tester

AEMC Clamp-On Ground Resistance Tester (Model 6417)

For more information about AEMC's products, please visit the AEMC website. To purchase products, visit your Baseline distributor.


Other Resources

AEMC's Soil Resistivity Report (used to plot the data gathered in the Fall of Potential Test)

 

AEMC's Technical Documentation for Ground Testers

 

AEMC's Tech Support Contact Information

  • 1 (508) 698-2115 (Ext. 351)
  • 1 (800) 343-1391 (Ext. 351)
  • techsupport@aemc.com